Articles | Volume 15, issue 15
Atmos. Chem. Phys., 15, 8975–8986, 2015
Atmos. Chem. Phys., 15, 8975–8986, 2015

Research article 13 Aug 2015

Research article | 13 Aug 2015

Hygroscopic and phase separation properties of ammonium sulfate/organics/water ternary solutions

M. A. Zawadowicz1, S. R. Proud1,2, S. S. Seppalainen1, and D. J. Cziczo1 M. A. Zawadowicz et al.
  • 1Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
  • 2University of Copenhagen, Copenhagen, Denmark

Abstract. Atmospheric aerosol particles are often partially or completely composed of inorganic salts, such as ammonium sulfate and sodium chloride, and therefore exhibit hygroscopic properties. Many inorganic salts have well-defined deliquescence and efflorescence points at which they take up and lose water, respectively. Field measurements have shown that atmospheric aerosols are not typically pure inorganic salt, instead, they often also contain organic species. There is ample evidence from laboratory studies that suggests that mixed particles exist in a phase-separated state, with an aqueous inorganic core and organic shell. Although phase separation has not been measured in situ, there is no reason it would not also take place in the atmosphere. Here, we investigate the deliquescence and efflorescence points, phase separation and ability to exchange gas-phase components of mixed organic and inorganic aerosol using a flow tube coupled with FTIR (Fourier transform infrared) spectroscopy. Ammonium sulfate aerosol mixed with organic polyols with different O : C ratios, including 1,4-butanediol, glycerol, 1,2,6-hexanetriol, 1,2-hexanediol, and 1,5-pentanediol have been investigated. Those constituents correspond to materials found in the atmosphere in great abundance and, therefore, particles prepared in this study should mimic atmospheric mixed-phase aerosol particles. Some results of this study tend to be in agreement with previous microscopy experiments, but others, such as phase separation properties of 1,2,6-hexanetriol, do not agree with previous work. Because the particles studied in this experiment are of a smaller size than those used in microscopy studies, the discrepancies found could be a size-related effect.

Short summary
This work investigates hygroscopic properties of internally mixed organic/inorganic aerosol particles. Aerosol particles containing organic and inorganic components can phase separate under certain relative humidity conditions, creating particles with an inorganic core and an organic shell. This paper explores whether water uptake from gaseous phase still occurs in such phase-separated systems. It finds that phase separation does not inhibit water uptake for the five systems that were studied.
Final-revised paper